Chemistry IGCSE - Acid, bases and salts

Acid reacting with alkaline

Acid + alkaline → water + salt

Acid reacting with base

Base + acid → water + salt

Acid reacting with carbonates

Carbonates + acid → water + salt + carbon dioxide

Acid reacting with metals

Metals + acid → salt + hydrogen

Acid reaction mnemonics

Indicators in litmus paper

Indicators in methyl orange

Bases are oxides or hydroxides of metals

Alkalis are soluble bases

Neutral solutions’ pHs

pH: 7.0

Colour: green

Acid solutions’ pH

pH < 7 → lower the pH → stronger the acid

Colour: changes from green → yellow → orange → red → acidity increases

Bases solutions’ pH

pH > 7 → higher the pH → stronger the alkali

Colour: changes from green → blue → purple → alkalinity increases

Acid

has H⁺ ions

Bases

has OH⁻ ions

Neutralisation

acid + alkali → salt + water

Metal oxide → basic oxide

basic oxides → e.g. CuO + CaO

Basic oxides → acidic oxides

acidic oxides → SO2 + CO2

Amphoteric oxides

oxides that react with acids + with bases → produces salt + water

→ e.g. Al2O3 + ZnO

Describe the preparation, separation + purification of soluble salts by reaction of an acid with: an alkali by titration

1. Pipette a measured volume of alkali into the flask, add indicator

2. Titrate with acid until indicator just changes colour → record volume used

3. Repeat → mix fresh alkali + exactly that volume of acid without indicator

4. Gently heat to concentrate → cool to crystallize

5. Filter off crystals, wash + dry

Describe the preparation, separation + purification of soluble salts by reaction of an acid with: excess metal

1. Add small pieces of metal to excess acid until bubbling stops

2. Filter to remove unreacted metal → collect clear filtrate

3. Heat to concentrate → cool to form crystals

4. Filter, wash + dry

Describe the preparation, separation + purification of soluble salts by reaction of an acid with: excess insoluble base

1. Stir excess solid base into the acid until no more dissolves

2. Filter off undissolved base → keep filtrate

3. Concentrate filtrate by gentle heating → cool to crystallize

4. Filter, wash + dry

Describe the preparation, separation + purification of soluble salts by reaction of an acid with: excess insoluble carbonate

1. Add excess carbonate to acid until CO₂ evolution ceases

2. Filter off leftover carbonate → clear filtrate remains

3. Gently heat to concentrate → allow to cool & crystallize

4. Filter crystals, wash + dry

Hydrated substance

a substance that is chemically combined with water

Anhydrous substance

a substance containing no water

Preparation of insoluble salts by precipitation

1. Dissolve soluble salts in water → mix together using a stirring rod in a beaker

• Filter to remove precipitate from mixture

• Wash the residue with distilled water → remove traces of other solutions

• Leave in an oven to dry